Surge protection device

ABSTRACT

A surge protection device includes a first electrode and a second electrode. An air breakdown spark gap is between the second and first electrodes, an arc being formed upon an ignition of the air breakdown spark gap. A series arrangement of a potential dividing element and an ignition element is connected to the first and second electrodes.

BACKGROUND

The invention relates to a surge protection arrangement, with a firstelectrode, with a second electrode, and with an existing or active airbreakdown spark gap between the two electrodes, whereby upon ignition ofthe air breakdown spark gap between the two electrodes, an arc arises.

Electrical, in particular, however, electronic measuring, control,regulating, and switch circuits, and also for telecommunicationarrangements and assemblies are susceptible to transient over-voltages,commonly called power surges, such as those than can occur throughatmospheric charges, or also through switch activity or short circuitsin energy supply networks. This susceptibility has been usedincreasingly in electronic components, in particular, transistors andthyristors; above all, integrated circuitries are increasinglyendangered in great numbers by transient power surges.

Electrical circuits work with the specified voltage, the rated voltage,normally failure-free. This is not the case when power surges occur.Power surges are all voltages, which lie above the upper tolerance limitof the rated voltage. In this regard, also the transient power surgesare counted, which based on atmospheric charges, however, also by switchactivity or short circuits, can occur in energy supply networks and canbe coupled galvanically, inductively, or capacitively in electriccircuitry. In order to protect electrical or electronic circuitryagainst power surges, in particular, electronic measuring, control,regulating, and switching circuits, as well as telecommunication unitsand assemblies, where also they are used, power surge protectionelements have been developed and have been known for more than 20 years.

Certain surge protection arrangements include at least one spark gap,which with a determined surge activates the operating voltage andtherewith prevents power surges from occurring in the circuitryprotected by a power surge protection element that are greater than theoperating voltage of the spark gap.

With air breakdown spark gaps, generally a breakdown spark gap is meant;included, then, also is a breakdown spark gap, with which not air, but adifferent gas, is provided between the electrodes. In addition to powersurge protection elements with an air flashover spark gap, power surgeprotection elements with an air flashover spark gap are provided, withwhich upon activation, a creepage charge occurs.

Power surge protection elements with an air breakdown spark gap, incontrast with power surge protection elements with an air flashoverspark gap, have the advantage of a higher surge current carryingcapacity, however, the disadvantage of a higher—and also not ratherconstant—operating voltage. Thus, already different power surgeprotection elements are proposed with an air breakdown spark gap, whichwith reference to the operating voltage, have been improved. In thismanner, in the area of the electrodes or the active air breakdown sparkgap between the electrodes, were realized in various manners with thesparking or ignition aids, for example, such between the electrodes, atleast one creepage charge releasing ignition aid was provided, which atleast partially projects into the air breakdown spark gap, is designedas graduated, and is made of plastic (compare, for example, the Germandisclosure documents 41 41 681 or 44 02 615).

The previously mentioned ignition or sparking aids with the known powersurge protection elements can be designated as “passive sparking aids”,“passive sparking aids” because they themselves do not activate“actively”, rather only by means of a power surge, which acts on themain electrode.

From the German published patent document 198 03 636, likewise a powersurge protection element with two electrodes is known, with an activeair breakdown spark gap between the two electrodes and an ignition orsparking aid. With this known power surge protection element, thesparking aid, in contrast to the previously mentioned types, forms acreepage charge releasing sparking aid as an “active sparking aid”,namely in that in addition to the two electrodes—here designated as mainelectrodes—two more sparking electrodes are provided. These two sparkingelectrodes form a second air breakdown spark gap, serving as an ignitionspark gap. With this known power surge protection element, an ignitioncircuit belongs to the ignition aid outside of the ignition spark gapwith an ignition switch element. Upon contact of a power surge to theknown power surge protection element, the ignition circuit with theignition switch element provides for an activation of the ignition sparkgap. The ignition spark gap or the two ignition electrodes are arrangedwith reference to the two main electrodes such that, thereby, it hasactivated the ignition spark gap, the air breakdown spark gap betweenthe two main electrodes, called the main spark gap, activates. Theactivation of the ignition spark gap leads to an ionization of the airprovided in the air breakdown spark gap, so that, abruptly, afteractivation of the ignition spark gap, then also the air breakdown sparkgap between the two main electrodes, that is, the main spark gap,activates.

With the known, previously described embodiments of power surgeprotection elements with ignition aids, the ignition aids lead to animproved, specifically lower and more constant operating voltage.

With surge protection arrangements of the type discussed—with or withoutan ignition air—upon ignition of the air breakdown spark gap alow-impeded connection arises between the two electrodes. Via thislow-impeded connection, first the lightning current to be dissipatedflows. With an adjacent network voltage, however, an undesired networksequence current follows via this low-impeded connection of the surgeprotection arrangement, so that one is anxious to extinguish the arc asquickly as possible after the completed arresting process. Onepossibility for achieving this goal is to enlarge the arc length andtherewith, the arc voltage.

One possibility for extinguishing or canceling the arc after thearresting process, namely, to enlarge the arc length and therewith thearc voltage, is realized with the surge protection arrangement, as isknown from the German published patent document 44 02 615. The surgeprotection arrangement known from this document has two narrowelectrodes, which, respectively, are angularly formed and which eachhave a spark horn and a connection leg angled therefrom. In addition,the spark horns for the electrodes are provided with a bore in theregions bordering the connection leg. The bores provided in the sparkhorns of the electrodes sees to it that in the moment of the activationof the surge protection element, that is of the ignition, the arisen arcis “put into motion”, that is, diffused away from its formationposition. Since the spark horns of the electrodes are arranged V-shapedrelative to one another, the gap to be bridged over from the arc, upondiffusing out of the arc, enlarges, whereby also the arc voltageincreases.

A further possibility for extinguishing the act after the arrestingprocess exists in the cooling of the arc by means of the cooling actionof insulation walls, as well as the use of gas-emitting insulation. Inthis manner, an intense flow of the extinguishing gas is necessary,which requires a high constructive expense.

If the arc is extinguished in surge protection arrangements of the typediscussed, then first, the low-impeded connection between the twoelectrodes is interrupted, the space between the two electrodes, thatis, the region of the air breakdown spark gap, is almost completelyfilled with plasma, however. By means of the existing plasma, however,the operating voltage between the two electrodes is lowered, such thatit can result in a renewed ignition of the air breakdown spark gapalready with an adjacent operating voltage. This problem occursparticularly, then, when the surge protection arrangement has anencapsulated or half-open housing, since then, a cooling or escape ofthe plasma is prevented by the essentially closed housing.

In order to prevent a renewed ignition of the surge protectionarrangement, that is, the air breakdown spark gap, different featureshave been proposed up to now, in order to drive away or cool the ionizedgas clouds from the ignition electrodes. In this connection,constructively expensive labyrinths and cooling bodies are used, wherebythe manufacture of the surge protection arrangement is made moreexpensive.

From the German published patent document 100 40 632, a surge protectionarrangement is known, in which a renewed activation of the air breakdownspark gap is prevented after the arresting process, which can berealized constructively simply. With this known surge protectionarrangement, it operates with a main spark gap, with an ancillary sparkgap, and with a housing accommodating the main spark gap and theancillary spark gap, whereby the main spark gap has a first mainelectrode, a second main electrode, and an existing or active airbreakdown spark gap between the main electrodes, and upon ignition ofthe air breakdown spark gap, an arc arises between the first mainelectrode and the second main electrode. The ancillary spark gap has afirst ancillary electrode, a second ancillary electrode and a second airbreakdown spark gap between the ancillary electrodes. An ignition of thetwo air breakdown spark gaps lead to an ignition of the first airbreakdown spark gap, whereby the second ancillary electrode, via atleast one impedance, is directly or indirectly connected with the secondmain electrode.

U.S. Pat. No. 5,436,608 describes a surge protection element, in whichthe operating voltage, or ignition voltage, is preset by the geometricdimension of the silicon chip. The ignition voltage is determined by theheight of a projection on the silicon chip, the projection being locatedin an insulated manner between an electrode and the silicon chip. Thisarrangement has the disadvantage that the operating voltage isaccomplished through accurate configuration of the height of theprojection. This requires high accuracy of manufacture; subsequentchange of the operating voltage is not possible. Moreover, theinsulating film required for this device can be damaged or destroyedwhen a power surge is discharged, as a result of which the surgeprotection element would be changed in its operating voltage to such anextent that it would no longer be functional.

Document JP 09266052 from Patent Abstracts of Japan describes a surgeprotection element, which is composed of two opposite electrodes havinga special shape, and in which a capacitive impedance, in particular acapacitor and a resistor, is connected between the electrodes. However,this arrangement is only able to discharge smaller surges, which do notyet produce any spark between the opposite electrodes. To ignite thespark gap between the opposite electrodes, the ignition voltage of thespark gap must be reached or exceeded.

German patent document DE 19510181 C1 describes a surge protectionelement, in which a first spark gap is used to trigger the flashover atthe second, that is, the main spark gap. In this context, the operatingvoltage of the first spark gap is set by the electrode spacing of thefirst spark gap and an impedance connected in series thereto. In thisarrangement too, an accurate dimensioning of the electrode spacing ofthe first spark gap is necessary for the adjustment of the ignitionvoltage.

French patent document FR 1105378 A described a surge protection elementincluding a main spark gap and a parallel ancillary spark gap with acapacitance. A capacitance is connected to the ancillary spark gap, thegeometric arrangement being designed in such a manner that an ignitedancillary spark gap will not ignite the main spark gap. Here, theancillary spark gap is intended to discharge smaller surges; the mainspark gap igniting automatically without ignition aid and only when alarger surge occurs.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a simple surgeprotection arrangement with a simply acting ignition aid.

According to the present invention, between the two electrodes, theseries connection of a potential dividing element and an ignitionelement is provided.

In this manner, a completely new surge protection device with anignition air or a completely new ignition aid in a surge protectionarrangement is realized, as is provided in the following description.

The potential dividing element is chosen or dimensioned such that withthe operating voltage, the surge protection arrangement is “switched”.As a potential dividing element, a varistor, a suppressor-diode, or agas-filled voltage arrestor can be provided. Also the possibilityexists, however, that as the potential dividing element, a combinationof a varistor and a suppressor diode, a combination of a varistor and agas-filled excess voltage suppressor, a combination of a suppressordiode and a gas-filled excess voltage suppressor or a combination of avaristor, a suppressor diode and a gas-filled excess voltage suppressoris provided. The ignition element is made of an electrically conductivematerial and is arc-resistant; in addition, the ignition element cannotbe welded or smelted with the electrode associated with it, that is,with the electrode with which it is in electrically conductive contact.Preferably, the ignition element and/or the electrode associated withthe ignition element are made from an electrically conductive ceramicmaterial, from a non-welded metallic material, and/or from anelectrically conductive plastic. Generally, it is preferred that betweenthe ignition element and the electrode associated with the ignitionelement a transition resistance is provide.

If a surge acts on the inventive sure protection arrangement, which isthe same or greater than the operating voltage provided by the potentialdividing element, then the potential dividing element activates, so thata leakage current begins to flow over the series connection firstelectrode—potential dividing element—ignition element—second electrode;surges with minimal energy content, then, are bled off via thepreviously described series connection. If the energy content is greaterthan the surge on the surge protection arrangement, a correspondinglygreater current flows. This current leads to discharge at the contactpoint between the ignition element and the associated element because ofthe high transition resistance on the contact point, which leads to apre-ionization of the contact region, so that an arc is formed whichbridges the contact point. Because of the not insubstantial resistanceof the ignition element, the arc migrates to the ignition element, onorder to bridge its resistance. This mechanism then leads to an ignitionof the air breakdown spark gap between the two electrodes, that is,between the two electrodes, an arc arises.

According to the present invention, then, a surge protection arrangementwith an ignition aid is provided, with which the operating voltage canbe adjusted in a simple manner in wide limits with minimal tolerances,namely, by the selection or dimensioning of the potential dividingelement. In this connection, the ignition aid with the inventive surgeprotection arrangement should not be susceptible to mechanical andthermal exposure and should be placeable directly inside of the sparkgap formed by the two electrodes. It is also important that with theinventive surge protection arrangement, a “passive ignition aid” wasrealized, that is, an additional ignition circuit—with an ignition pulsegenerator—is not required.

BRIEF DESCRIPTION OF THE DRAWINGS

In detail, a multitude of possibilities exist for constructing andfurther embodying the inventive surge protection arrangement. In thisconnection, reference is made to the claims that depend on claim 1, aswell as the following description of embodiments with reference to thedrawings. In the drawings:

FIG. 1 shows a schematic representation of a first embodiment of thesurge protection device of the present invention; and

FIG. 2 shows a schematic representation of a second embodiment of thesurge protection device of the present invention.

DETAILED DESCRIPTION

In FIGS. 1 and 2, respectively, a surge protection arrangement of thepresent invention is shown only with reference to their principalstructure. Each shown surge protection arrangement includes a firstelectrode 1, a second electrode 2, and an existing or active airbreakdown spark gap 3 between the two electrodes. For the inventivesurge protection arrangements, as with the surge protection arrangementson which the invention is based, upon ignition of the air breakdownspark gap 3 between the two electrodes 1 and 2, an arc—not shown—arises.

According to the present invention, the series connection of a potentialdividing element 4 and an ignition element 5 is connected to the twoelectrodes 1 and 2.

In FIGS. 1 and 2, the potential dividing element 4 is only schematicallyshown. As a potential dividing element 4, with which the operatingvoltage of the inventive surge protection arrangement is provided, avaristor, a suppressor diode, or a gas-filled voltage suppressor can beprovided. However, also the possibility exists that as a potentialdividing element 4, a combination of a varistor and a suppressor diode,a combination of a varistor and a gas-filled excess voltage suppressor,a combination of a suppressor diode and a gas-filled excess voltagesuppressor or a combination of a varistor, a suppressor diode and agas-filled excess voltage suppressor can be provided.

Like the potential dividing element 4, also the ignition element 5 ofsurge protection arrangement shown in FIGS. 1 and 2 only schematicallyshown. The ignition element 5 is made from a material, which iselectrically conductive and arc-resistant. In addition, the ignitionelement 5 cannot be welded to the contact point 6 of the electrode 2with the electrode 2. Preferably, the ignition element 5 and/or theelectrode 2 associated with the ignition element 5 is made from anelectrically conductive ceramic material, from a non-welded metallicmaterial and/or form an electrically conductive plastic.

In detail, a transition resistance is provided permanently between theignition element 5 and the electrode 2 associated with the ignitionelement 5; the contact point 6, then, has a permanent transitionresistance. This transition resistance can be realized through anappropriate selection of the electrical conductivity of the materials ofthe ignition element 5 and/or the electrode 2 associated with theignition element 5, preferably by an appropriate selection of thematerial of the ignition element 5. The transition resistance providedpermanently on the contact point 6 can be realized by an appropriateselection of the electrical conductivity of the materials of theignition element 5 and/or the electrode 2 associated with the ignitionelement 5, or additionally, by an appropriate geometric formation of theignition element 5 on the contact point 6 to the associated electrode 2and/or by an appropriate geometric formation of the electrode 2 on thecontact point 6 for the ignition element 5, preferably by a smallcontact surface.

The contact surface 6 between the ignition element 6 and the associatedelectrode 2, particularly, has a small contact surface then, when theignition element 5 on its end associated with the electrode 2 ispunctiform or cutting-formed and the electrode 2 is convexly formed onits side facing the ignition element 5. With the geometric realizationof the contact point 6 between the ignition element 5 and the electrode2, however, it should also be noted that the air gap following thecontact point 6 that is between the ignition element 5 and the electrode2, two criteria, with regard to electrical considerations, are met.First, the air gap is large enough so that with a surge with minimalenergy content, the leakage current flows only over the contact point 6,that is, the contact region encompassing the contact point 6,experiences no pre-ionization. Second, the air gap is small enough sothat, when the energy content of the surge is greater, the flowingcurrent leads to a pre-ionization of the contact region encompassing thecontact point 6. A solution, which meets the two criteria, is realizedwith the shown embodiments. In this manner, the end of the ignitionelement 5 facing the electrode 2 is cone-shaped convexly and the side ofthe electrode 2 facing the ignition element 5 is cone-shaped concavely.

FIGS. 1 and 2 show that with the preferred embodiments of the presentinvention, the contact pressure between the ignition element 5 and theassociated electrode 2 is adjustable. In the embodiments, this isrealized by means of a pressure spring 7 acting on the ignition element5, with pressure springs 7, different types of spring being useable fordifferent contact pressures. However, also the non-illustratedpossibility exists to make the contact pressure between the ignitionelement 5 and the associated electrode 2 adjustable by means of amechanically reversible deformable material of the ignition element 5and/or at least one electrode, preferably, the electrode 2 associatedwith the ignition element 5.

As noted above, with the inventive surge protection device, a seriesconnection of a potential dividing element 4 and an ignition element 5is provided between the two electrodes 1 and 2. What is meant is anelectrical series connection, not implicitly mechanical or spatial orgeometric.

In the embodiment of the inventive surge protection arrangement shownschematically in FIG. 1, the potential dividing element 4 as well as theignition element 5 is provided spatially between the two electrodes 1and 2. In addition, FIG. 2 shows an embodiment, in which the potentialdividing element 4 is arranged spatially outside of the region betweenthe two electrodes 1 and 2. With this embodiment, the potential dividingelement 5 arranged outside of the region between the two electrodes 1and 2, on one side, is connected with the electrode 2 via an outerconnecting element 8 and on the other side, is connected via aconnection pin 9 with the—electrically conducting—pressure spring 7, andtherewith, with the ignition element 5.

1. A surge protection device comprising: a first electrode; a secondelectrode, the second and first electrodes forming an air breakdownspark gap therebetween, the air breakdown spark gap being configured sothat an arc occurs upon an ignition of the air breakdown spark gap; anda series arrangement of a potential dividing element and an ignitionelement, the series arrangement being connected to the first and secondelectrodes; wherein the ignition element and the second electrode have acontact region so as to provide a permanent transition resistance; andwherein the second electrode is associated with the ignition element anda contact pressure between the ignition element and the associatedelectrode is adjustable.
 2. The surge protection device as recited inclaim 1 wherein the contact pressure is adjustable using at least one ofa pressure spring acting on the ignition element, a mechanicallyreversible deformability of a material of the ignition element, and amechanically reversible deformability of a material of at least one ofthe first and second electrode.
 3. The surge protection device asrecited in claim 2 wherein the contact pressure is adjustable using amechanically reversible deformability of a material of the secondelectrode.
 4. A surge protection device comprising: a first electrode; asecond electrode, the second and first electrodes forming an airbreakdown spark gap therebetween, the air breakdown spark gap beingconfigured so that an arc occurs upon an ignition of the air breakdownspark gap; and a series arrangement of a potential dividing element andan ignition element, the series arrangement being connected to the firstand second electrodes; wherein the second electrode is associated withthe ignition element and a contact pressure between the ignition elementand the associated electrode is adjustable using at least one of apressure spring acting on the ignition element, a mechanicallyreversible deformability of a material of the ignition element, and amechanically reversible deformability of a material of at least one ofthe first and second electrode.
 5. The surge protection device asrecited in claim 4 wherein the contact pressure is adjustable using amechanically reversible deformability of a material of the secondelectrode.